The impression I've gotten is that Cold Steel II does conclude certain things begun in the first game and doesn't necessarily end in the kind of cliffhanger Cold Steel I does, which leaves you right in the middle of dramatic things happening, but overall is not quite as conclusive an ending to the Cold Steel saga as SC is to the storyline begun in TitS FC, leaving things more open for another game in Erebonia.
I mean, there's surely a reason why XSeed felt confident in releasing a Cold Steel Collector's Edition box that only has room the first two games. I assume that means the first two games do tell a somewhat self-contained story arc, even if maybe the larger conflict isn't completely resolved.
If you can hold yourself from playing the first game, it's not a bad idea to wait until CSII is closer to release before playing the game (though the first game can easily take 70-80 hours to complete just once, so time its playthrough accordingly). Not sure if it'd then be wise to still wait even longer until Cold Steel III before playing 1 & 2. I & II have so much content combined that you'll probably burn out trying to play three Kiseki games in a row. Probably good to have SOME space between the playthroughs of the Cold Steel games, just so that you aren't sick of it all by the time you get to CSIII.